This invention was made in the course of, or under, a contract with the Energy Research and Development Administration. The present invention is generally a continuous flow centrifuge rotor, and more specifically a closed-type continuous flow centrifuge rotor.
Human leucocytes (white blood cells) are found in several varieties. Granulocytes are leucocytes which are phagocytic and protect the body against infection. In some forms of leukemia, while the patient has a superabundancy of granulocytes, for the most part they are immature and incapable of carrying out their phagocytic function. Accordingly, death in human leukemia is most frequently attributable to infections in patients with a deficiency of mature granulocytes. Ganulocyte replacement therapy can reverse the usual course of infection in such patients.
In order to carry out granulocyte replacement it is necessary to remove transfusible quantities of white blood cells from a donor's blood and introduce the white cells into the patient. While this can be done with a sequential batch-type separation technique, it is impractical because a human donor can have only about one liter of blood removed at a time without risking harm to himself. However, the normal human body is capable of producing granulocytes whenever they are needed and indeed this is what happens when a normal human acquires an infection.
This fact makes a continuous granulocyte separation process most attractive. Blood is removed continuously from a healthy donor, centrifuged to remove the white cells, and the remainder of the blood is continuously returned to the donor. The centrifuge is designed to require a volume of no more than about one liter of blood, hence the donor is never deprived of more than about one liter of blood at any time. The separated white cells are introduced into the patient. The performance of centrifuges used for this separation varies widely from donor to donor, and the yield of white cells obtained has not been entirely satisfactory. Therefore, granulocyte replacement therapy has not been widely adopted.
The centrifugal separation of blood components is based upon an application of Stoke's law. Stoke's law states in part that the sedimentation of particles in a suspending medium is directly proportional to the size and density of the particles. In whole blood, the red cells tend to form rouleaux (agglomerates) which are larger than the white cells. Therefore, red cell rouleaux will sediment faster than white cells. When whole blood is placed in a centrifuge, the centrifugal field causes the components to separate into three zones, an outer zone of red cell rouleaux, an intermediate zone of white cells, and an inner zone of plasma.
One of the most important problems encountered in blood centrifuges is that the shear stress in the separation chamber is so large that red cell rouleaux are broken up, and hence no longer easily separable from the white cells. This shear stress may be conveniently expressed as a fluid velocity gradient within the channels of the rotor. It is measured in units of velocity per unit distance, and has the dimensions of sec.sup.-.sub.1. In addition, Coriolis forces acting on the particles as they sediment away from the axis of rotation may cause convective mixing between the phases. In normal blood, velocity gradients of about 5 sec.sup.-.sup.1 or less are generally required to maintain appreciable red cell rouleaux structure.